1. Field of the Invention
The present invention relates to a photosensitive composition, and more particularly to a photosensitive composition capable of giving a negative type polyimide pattern upon development with an aqueous alkaline solution.
2. Description of Related Art
So far used photosensitive resins are typically polyester acrylate, epoxy acrylate, etc. To obtain a desired pattern upon exposure of these photosensitive resins to light, an organic solvent is used as a developing agent. Such organic solvent developing type, photosensitive resins have such a serious problem as an adverse effect on the environments in addition to safety or sanitary problem during working due to the use of the organic solvent.
In place of the organic solvent developing type, photosensitive resins having such problems, alkali-developable photosensitive resins based on novolak resins, polyvinylphenol, etc. have been proposed and almost all of them have been utilized as positive type thin films having a thickness of a several .mu.m, but these positive type thin films have not always satisfied the heat resistance, preservation stability, pattern embedability, etc. required by FPC (flexible printed substrate) applications.
Furthermore, polyimide resins themselves are insoluble in an organic solvent and therefore have so far relied on such a method of once converting them to organic solvent-soluble polyamic acids, followed by their polyimidization. However, some of polyimide resins themselves are soluble in an organic solvent. For example, polyimide resins disclosed in JP-A-57-131227 and polyamide-imide resins disclosed in JP-A-59-145216 are said to be soluble in an organic solvent and photosensitive. However, the organic solvent for that purpose is aprotic polar solvents including dimethyl-formamide, whereas acetone, benzene, cyclohexanol, etc., on the other hand, are used there for deposition of the resins. That is, the resins are insoluble in these latter organic solvents.